The same inventors as those of the present invention proposed a catalyst for use in purifying exhaust gas, said catalyst comprising manganese dioxide, calcium aluminate and heat resistant aggregate. This catalyst has been disclosed in U.S. Pat. No. 3,905,917. The inventors have found that a catalyst comprising a mixture of manganese dioxide, calcium aluminate, iron oxyhydroxide and copper hydroxycarbonate and a catalyst prepared by heating said mixture are superior to the catalyst disclosed in U.S. Pat. No. 3,905,917 in the catalytic action of oxidation of carbon monoxide, nitrogen monoxide or sulfur dioxide. The present invention is based on this discovery.